Scandium was discovered in 1879, and was first isolated as the pure metal in 1937 by the high temperature electrolysis of a eutectic mixture of potassium, lithium and scandium chlorides. For much of its history, scandium remained a commercially insignificant metal with few known practical uses. More recently, however, a number of uses of scandium have been identified, and commercial interest in the metal has increased. For example, scandia-stabilized zirconia has gained importance as a high efficiency electrolyte in solid oxide fuel cells, while scandium oxide (scandia or Sc2O3) has found use in high intensity discharge lamps. Scandium alloys, and especially scandium aluminum alloys, have attracted interest in various aerospace applications, as demonstrated by their use in the MiG-21 and MiG-29 aircraft.
Scandium alloys offer numerous advantages over other metal alloys in various applications. For example, some scandium-reinforced alloys are much stronger than their non-scandium counterparts. Moreover, the use of scandium in some metal alloys significantly improves the grain refinement of the alloys, eliminates hot cracking and improves strength in welds. Scandium alloys also exhibit good resistance to corrosion.
Scandium-aluminum alloys are of particular commercial interest, since these alloys exhibit a lower specific gravity compared to the more widely used titanium aluminum alloys. Thus, for example, Sc—Al has a specific gravity of 2.8 compared to 4.5 for Ti6Al4V. In a commercial airline fleet, this difference in specific gravity translates into substantial fuel savings on an annual basis.
Despite the many advantages they have to offer, the widespread use of scandium and its alloys has been hampered by the low availability (and consequently high cost) of the element. Although scandium is not a particularly rare metal in terms of its abundance in the Earth's crust, there are currently no known, easily extractable deposits of minerals which contain high concentrations of the metal. Consequently, most scandium today is obtained as a byproduct of other metal recovery processes, typically from the treatment of tailings or metal sludges obtained from the refining of other metals. For example, scandium is frequently recovered as a byproduct of the treatment of tungsten and uranium tailings, or from waste streams resulting from the processing of titanium-containing ores and concentrates into titanium dioxide pigments. Scandium may also be obtained from the treatment of red mud, which is a waste product of the Bayer process used to refine bauxite into alumina.